(i) Field of the Invention:
This invention relates to azo pigment compositions which are adapted for use as printing inks or paints having good fluidity, coloring power (color strength), transparency and gloss.
(ii) Description of the Prior Art
Naphthol-type azo pigments have been widely used in the manufacture of printing inks, paints and the like. They are disadvantageous in that during the manufacture or storage of printing inks or paints, solvents and binders contained in the inks or paints are interacted with the pigments, thereby causing undesirable flocculation of pigment particles and growth of crystals. As a result, there arises the serious problem in practical applications that the inks or paints involve an increase of viscosity, and lowerings of coloring power, transparency and gloss.
In order to solve the problem, attempts have been heretofore made including addition of flocculation inhibitors, surface treatment of pigments with various resins or surface active agents, and the like. However, these methods are not necessarily satisfactory for overcoming the disadvantages.
Another method of solving the above problem has been proposed such as, for example, in Japanese Patent Publication No. 44-18588. In this patent, it is stated that printing inks or paints can be kept low in viscosity and can prevent an increase of viscosity during storage when using phthalimidomethylation compounds of naphthol AS compounds and carboxylic acid compounds obtained by hydrolysis of the resulting methylated compounds, sulfonic acid compounds obtained by reaction of naphthol AS compounds with sulfuric acid, or alkaline earth metal salts or organic amine salts thereof. However, this method is not sufficient to solve the above problem.
Japanese Patent Publication No. 55-10630 describes a method of improving recrystallization stability of monoazo pigments in printing inks by way of co-coupling with a coupling component having an acidic group. However, the improvement is not adequate.